LHC MAGNET POLARITIES

Transcription

1 CEN CH-1211 Geneva 23 Switzerland the Large Hadron Collider project 9LHC Project Document No. CEN Div./Group or Supplier/Contractor Document No. AB/CO, LHC/TCP, AT/MEL EDMS Document No Date: Engineering Specification LHC MAGNET POLAITIES Abstract The aim of this document is to specify the current to field relationship in the LHC magnets. It defines the resultant field for a current entering a given terminal. A simple set of rules is given followed by diagrams demonstrating its application to each type of magnet Prepared by : Paul Proudlock LHC/TCP Stephan ussenschuck AT/MEL Markus Zerlauth AB/CO Checked by : M. Buzio L. Bottura O. Bruning J-L. Perinet-Marquet. Ostojic G. De ijk L. ossi. Schmidt T. Tortchanoff L. Walckiers. Wolf Original version 1.0 approved by: TCC on P&LC on evised version 3.2 approved by: udiger Schmidt Oliver Bruning

2 Page 2 of 15 History of Changes ev. No. (draft) Date Pages Description of Changes First draft of document no. LHC-DC-ES (draft2) Second draft of document no. LHC-DC-ES rev Document approved by P&LC on 10 June 1998 rev Addition of paragraph 6 rev Additions paragraph 7, 8, 9, 10 rev First submission for engineering check rev Modifications: paragraph 3, 7 rev All evised version 2.0: eleased ev Modifications of paragraph 10: title and 2 nd. All evised version 2.1: eleased ev ,14 Modifications chapter 10, addition chapter 11 ev All evised by Stephan ussenschuck as LHC Magnet Polarity Coordinator Page 4: emoved B1 and B2 notation, replaced by Dipole / Quadrupole to avoid confusion (B1 and B2 are only well defined in a reference frame) Page 5: emoved A1 and A2 notation, replaced by Skew Dipole / Skew Quadrupole, removed erroneous paragraph 6. Page 6: emoved B1 and A1 notation in the upper drawing, replaced by dipole / skew dipole. Note that the definition is not coherent with the definitions in MAD or in the magnet calculation and measurement frame. Page 7: emoved B2 and A2 notation in the lower drawing Page 8: emoved B3 and A3 notation in the lower drawing Page 9: emoved A4, B4, and B5 notation in both drawings Page 10, 11: emoved B1, B3, B4, and B5 notation in drawing, text and table All Submission for engineering check All Changing the term magnets into main magnets in sections 4 and 7.1 emoving the sentence on spool piece magnets in section 7.1 eleased version All Minor modifications New eleased version Adding chapter on experimental magnets and compensators (section 6.1) New eleased version

3 Page 3 of 15 Table of Contents 1. EFEENCE DOCUMENTS INTODUCTION BASIC ULES SPECIAL CASE FO TUNED MAGNETS APPLICATION OF THE ULES CONNECTION OF COECTO MAGNETS EXPEIMENTAL MAGNETS AND COMPENSATOS TUNED MAGNETS SPECIAL CASE FO THE SPOOL SPIECES OF TUNED MAGNETS TWIN APETUE QUADUPOLE WITH SAME FUNCTIONS SINGLE APETUE MAGNETS COVEING BOTH BEAMS LABELLING OF CUENT LEADS ON A DFB (ELECTICAL FEEDBOX) POLAITY CONVENTIONS FO THE MAD SEQUENCE FILE EFEENCES...15

4 Page 4 of EFEENCE DOCUMENTS Minutes of the TCC meeting of 27 February Minutes of the P&LC meeting of 10 June Error Naming Conventions for LHC Magnets LHC-M-ES INTODUCTION The following basic set of rules is conceived to give a simple method of identification of the magnet polarities as installed in the tunnel independent of the applied reference frames. It allows magnets of a given type to be manufactured and assembled without prior knowledge of its position or function in the machine. The final polarity of the operating current, and thus the optical function of the magnet, will be obtained by choosing the correct connection on the warm side of the machine. This set of rules does not follow the conventions of the beam optics program MAD or the conventions for magnetic field computations and measurements. Appropriate transformations into the MAD or measurement reference frames have to be applied. 3. BASIC ULES The magnet terminals and the current leads to which they are connected will be marked with A and B (not + and - ). The fields and gradients are positive if the current enters the A terminal. Positive field means an upward pointing field direction while positive gradient is an increasing field along the outward pointing machine radius. The figures show the vertical field component. Power Converter I A B Magnet aperture aperture Center of machine Dipole Quadrupole

5 Page 5 of Skew magnets are tilted clockwise by an angle of 90 /n The rules apply to both internal and external apertures. Twin aperture magnets often have only one pair of terminals serving the two apertures. In the case of conflict (e.g. the main dipoles), the external aperture takes priority for the application of the rules. The set of rules applies to the magnets as installed in the machine and therefore ignores at which end the connections are placed. It is supposed that each magnet will be installed in the same direction. (See paragraph 4 below for special case.) 4. SPECIAL CASE FO TUNED MAGNETS In general, magnets are installed facing the same (normal) direction around the machine with their connections at any end of the magnet. However, a few magnets will be turned to face the opposite direction. If this occurs, the magnet is identical to the normal facing magnets and the terminal markings remain the same. Compensation for the resultant change of polarity, violating the basic rules, is made by an appropriate change of connection on the warm side. 5. APPLICATION OF THE ULES Examples of the application of the above rules to the LHC magnets are given in the following illustrations. They define the resultant field and optical function for all types of LHC magnets, considering the direction of the beam and the terminal into which the current enters. The illustrations are made looking in direction of beam 1 (circulating clockwise) with the machine centre to the right. is taken as the clockwise rotating beam and beam 2 as the anti-clockwise. is in the external aperture in sectors 1-2, 5-6, 6-7, 7-8, while beam 2 is in the external aperture in sectors 2-3, 3-4, 4-5, 8-1.

6 Page 6 of 15 TWIN APETUE MAIN DIPOLES Current into Terminal A Sectors: 1-2, 5-6, 6-7, 7-8 Current into Terminal B Sectors: 2-3, 3-4, 4-5, 8-1

7 Page 7 of 15 TWIN APETUE SEPAATO DIPOLES Current into Terminal A Current into Terminal B Sectors:- 1-2, 5-6, 6-7, 7-8 Sectors:- 2-3, 3-4, 4-5, 8-1

8 Page 8 of 15 TWIN APETUE MAIN QUADUPOLES Current into Terminal A Current into Terminal B (clockwise) Focusing (anti-clock.) Defocusing Sectors:- 1-2, 5-6, 6-7, 7-8 (clockwise) Defocusing (anti-clock.) Focusing (anti-clock.) Defocusing (clockwise) Focusing Sectors:- 2-3, 3-4, 4-5, 8-1 (anti-clock.) Focusing (clockwise) Defocusing

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10 6. CONNECTION OF COECTO MAGNETS LHC Project Document No. Page 10 of 15 Corrector magnets used to correct field errors in a magnet are powered in such a way that their vertical field component in the outer part of the aperture points in the same direction as the main field component when the bipolar power converter for the corrector circuit is in "positive" polarity. Should a fixed polarity power converter be used for an error of fixed polarity then it must be connected so as to cancel the error. This will need a treatment on a case-by-case basis. Applying this to the correctors of the main dipoles and following this convention implies that the correctors of beam 1 (clockwise) always have their current entering the terminal A, while the correctors of beam 2 always have their current entering terminal B for a positive current from the power converter. Hence for the powering of the machine: When beam 1 is in the external aperture (sectors 1-2, 5-6, 6-7, 7-8) Main dipole current enters the A terminal. For the spool pieces of the external aperture, current enters the A terminal. For the spool pieces of the internal aperture, current enters the B terminal. When beam 2 is in the external aperture, (sectors 2-3, 3-4, 4-5, 8-1) Main dipole current enters the B terminal. For the spool pieces of the external aperture, current enters the B terminal. For the spool pieces of the internal aperture, current enters the A terminal.

11 Page 11 of EXPEIMENTAL MAGNETS AND COMPENSATOS The conventions defined for magnets of the LHC machine will also be valid for the normal conducting experimental magnets and their compensators. The experiments in these insertion points use spectrometer (dipole) magnets which distort the beam trajectories. This effect is locally compensated with three orbit correctors placed in the straight sections between the interaction point and the final focussing triplet. As an example, the electrical layouts of the spectrometer dipole magnet compensations in I2 and I8 are shown in the following figure: The compensators are powered according to the rules for the orbit correctors in the arc, i.e., a positive kick (upwards or outwards) on is obtained by a positive setting on the bi-polar power supply and the current entering the B terminal of the compensators. Notice the change of polarity for the turned, vertically deflecting magnet MBXWT in I2 while the turned, horizontally deflecting magnet MBXWS keeps its optical function (see also section 7 on turned magnets).

12 Page 12 of TUNED MAGNETS Magnets are placed in the machine in what is known as normal direction. For various reasons a magnet may be turned with respect to its normal direction in the machine. The physical construction and electrical connections of these magnets are not changed, but their optical function may change. While a magnet with an odd harmonic (dipole, sextupole ) does not change its optical function when turned, a magnet with an even harmonic (quadrupole, octupole ) does. The opposite is the case for skew magnets where the odd harmonics (vertical deflection dipole, skew sextupole ) change function and the even (skew quadrupole, skew octupole) do not. If there is a change of function then the magnet polarity must be inverted on the warm side in order to correct this. The table below summarises the situation. Dipole: no change Quadrupole: inverted Sextupole: no change Octupole: inverted Decapole: no change Dodepole: inverted Skew Dipole: inverted Skew Quadrupole: no change Skew Sextupole: inverted Skew Octupole: no change Skew Decapole: inverted Skew Dodepole: no change 7.1 SPECIAL CASE FO THE SPOOL SPIECES OF TUNED MAGNETS Spool piece magnets are installed in larger magnet assemblies (main dipoles and main quadrupoles). Some of the magnet assemblies are installed turned and their optical function may change. However, the field error of the magnet with respect to the main field does not change. If the optical function of the magnet assembly should remain unchanged when the magnet is turned, three cases are distinguished: Dipole magnet with vertical field direction the polarity remains Dipole magnet with horizontal field direction the polarity must change Quadrupole magnet the polarity must change If the polarity of the main magnet changes, the polarity of the spool piece magnet has also to be changed.

13 8. TWIN APETUE QUADUPOLE WITH SAME FUNCTIONS Page 13 of 15 In most cases in LHC, the optical function in each aperture of twin aperture quadrupole is opposite. There are exceptions. In this case the polarity convention is given below: TWIN APETUE QUADUPOLES WITH SAME FUNCTION Terminal A Terminal B QF QF QD QD QD QD QF QF 9. SINGLE APETUE MAGNETS COVEING BOTH BEAMS Where both beams pass through a single aperture magnet beam 1 (clockwise) is used to define the polarity. 10. LABELLING OF CUENT LEADS ON A DFB (ELECTICAL FEEDBOX) For magnets operating at cryogenic temperatures, the currents are fed into the cryostats via current leads, mounted on four different types of electrical feed boxes (DFBA, DFBM, DFBL and DFBX). Every electrical circuit powering LHC magnets uses two current leads, except the individually powered quadrupoles (MQM, MQY) which uses a third current lead for the common return busbar, and the main inner triplet circuits which use four current leads due to the embedded power converters. The assignment of current leads to the electrical circuits has been specified for all DFBs [1] [2] [3] [4]. Each current lead is given a unique name and index (according to its location on the DFB) and the name and pole of power converter that is connected to this lead. The polarity definition of a current lead on a DFB is derived from the magnet terminal it is connected to at its cold end. The current lead that is connected to the A terminal of the magnet takes the name of this terminal (A). The other lead is B.

14 Page 14 of 15 In case of the individually powered quadrupoles with a common return busbar and the mid-point connection of the spool-piece sextupole corrector circuits, this third lead is called C. 11. POLAITY CONVENTIONS FO THE MAD SEQUENCE FILE The LHC eference Database will allow for an automatic generation of the MAD sequence file. Based on the current version of physical and electrical layout data it will generate the sequence file for the optics program. Together with the strength file, used to define the numerical values of the strength constants defined in the sequence file, it will provide the complete input data needed for a MAD simulation. The sequence file will contain the sequence of LHC magnets around the LHC circumference and an according strength constant. The strength constant is identical for all magnets powered in one electrical circuit, while the sign of this strength constant is depending on the connection of the magnet within the circuit (current is entering terminal A or terminal B). As defined in this specification, a positive field or field gradient of the magnet will correspond to the definition of a positive strength constant in the sequence file 1. A negative field or field gradient of the magnet will be taken into account by defining a strength constant of negative sign in the sequence file. The numerical value for each strength constant defined in the sequence file can be found in the strength file. In general, the polarity convention as explained will be applied for the generation of the sequence file. Still, the large number of existing strength files used by AB-ABP are based on a slightly different convention, defining negative numerical values for some of the strength constants. These negative values will require an inversion of sign for the strength constant in the MAD sequence file (with respect to the previous definition) for the following electrical circuits (and as such magnets): Defocusing circuits of the type OD, SD1 and SD2 (containing sextupole and octupole magnets of the type MS and MO) will require an inversion of the sign for the strength constant in the MAD sequence file Defocusing main quadrupole magnets MQ in the circuits Q will require an inversion of the sign for the strength constant in the MAD sequence file. Exceptions to this case are the warm twin aperture quadrupoles MQWA used as Q4 and Q5 in the insertions 3 and 7 (see next item) The warm twin aperture magnets MQWA, connected in the circuits Q4 and Q5 in the insertions 3 and 7 will be given a positive strength constant in the MAD sequence file when installed left of the IP and a negative strength constant when installed at the right side of the IP The inner triplet (Q1 to Q3 in insertions 1,2,5 and 8) is powered via a set of embedded power converters and the strength constant assigned to each individual magnet will consequently be a sum of several single power converter strengths (valid for magnets of type MQXA and MQXB). Magnets of this type appear in the circuit types QX, TQX1 and TQX2, the resulting strengths in e.g. left of I2 will look as follows: 1 Positive indicates upward pointing field direction while positive gradient is an increasing field along the outward pointing machine radius.

15 Page 15 of 15 Q3 (MQXA): Q2 (2 MQXB): Q1 (MQXA): K1:= kqx.l2; K1:= -kqx.l2-kqxt2.l2; K1:= kqx.l2+kqxt1.l2; Some strengths of dipole orbit corrector magnets are defined as angles in the MAD sequence file and are to be entered by definition as positive values in the sequence file 12. EFEENCES [1] M. Zerlauth et al.: Current Lead Assignment on the DFBAs, EDMS Doc.Nr.: [2] M. Zerlauth et al.: Current Lead Assignment on the DFBLs, EDMS Doc.Nr.: [3] M. Zerlauth et al.: Current Lead Assignment on the DFBMs, EDMS Doc.Nr.: [4] J.Jzbasnik et al.: Inner Triple Feedboxes DFBX-Power Converters, EDMS Doc.Nr.: